Sudden Coolant loss—I don't think it's the head gasket

Engine Coolant water pump is my guess. Same problem I had maybe about a year ago now.

 

You'll see pink crusties if it's leaking at the pump.

 

Here is my theory:
The OP has a water pump impeller that is occasionally seizing (binding) OR the thermostat is not opening correctly and the reduced coolant flow causes the engine to overheat and the dash light to come on. When the engine overheats, the pressure in the coolant system increases to the point that coolant is forced past the screwed on lid on top of the plastic coolant tank and it comes out the little overflow tube that is just below the lid facing the back side of the tank. I just took a look at my car and the overflow tube has a small rubber cap that I assume is there to keep dirt from entering the tube. So this is why the coolant is disappearing from the Op's car.

Here is a picture of my coolant tank showing the black rubber cap on the overflow tube.



@CloudJumper , Take a look around your coolant tank and see if there is any dried pink residue or evidence of coolant overflow.

 

I am a novice in using TechStream and Torque Pro, so I am not much help. Maybe someone else with more experience is willing to help you. I know "just" enough to get myself into trouble while working on my car.

Can you please give us some history on your car. Are you the original owner? Has the engine coolant, water pump, thermostat ever been replaced?

 

In my case, coolant was coming out of the engine coolant reservoir that shows max/ min levels. At first I thought I had a bad cap.

Told my mechanic and he just topped it off. He said next time it happens, to take it to his shop right away so he can plug it in for diagnostics.

happened again and I was able to take it to him as instructed. His OBDII computer readings read a bad engine coolant water pump.

Went to the dealer and replaced it, along with the thermostat for good measures.

 

Just for giggles, boroscope the cylinders with the cooling system pressurized, look for coolant "tears"? I know, but it's third gen...

 

I am impressed with the number of coolant replacements that you had done. Sounds like you take very good care of your car.

When the water pump impeller binds up and runs slower then required, you will get a P261B trouble code. I am guessing that your water pump is not to the point of setting this code but I would advise you to get it replaced ASAP. I would also get the thermostat replaced at the same time, because it is good insurance even if it is not needed. It does not cost very much more.

The engine over temperature dash light comes on at a fairly high temperature. I do not remember at what temperature, but you can search the Gen 3 forum. In my opinion, it should have been set for a lower temperature.

I believe the majority of head gasket failures on a Gen 3 are caused by the engine overheating because of water pump failures. I have a P10 display unit plugged into the OBDII port so that I can watch my water temperature and voltage level. I never liked that there was no water temperature gauge included in the instrument panel.

 

Same here.

 

Because of the degas-bottle cooling system style, there is quite a bit of headspace in the coolant bottle. Even if the coolant ever gets hot enough to exceed the 108 kPa relief point of the cap, there's a bunch of air up there that would be first to escape, before it comes to any coolant escaping. (The air will carry a bit of vapor, of course.)

There are two temperature sensors that can trigger the red-thermometer light. I tested one and found the light to come on at 120 ℃. I assume it's the same for the other one, but I haven't tested that.

If any of the water pump trouble codes are set, the ECM will silently, without warning, shut down the engine if it reaches 105 ℃.

 

I could not find the original invoice but since it’s the stealership, I remember the cost at $1k +\- , for parts & labor.

Definitely wasn’t cheap but it was well worth it, if done right. I replaced mine at about 175k miles on August 2020. The car is closing in on 220k miles and still going strong.

 

I’m in California. Bay Area. Everything is expensive in my location. It was for sure over $750.

 

Time out… Now I’m ultimately confused. (Please don’t take this personally I just got my concept of hotter plug corrected). So we are concerned that the EGR plugged causes the engine to run hotter (please correct me if I’m wrong, but now the “hotter plug” seems to contradict that concern?


iPhone ?